The present invention pertains to a method and a device for detecting a filling process.
When monitoring the level of free-flowing or pourable materials, one frequently utilizes sensors that emit a signal into the container, receive reflected signals from the container and make it possible to estimate the level in the container by means of a signal analysis.
These sensors function satisfactorily as long as the level in the interior of the container does not vary to a significant degree such that a well defined surface of the material exists. The contribution of this well defined surface to the echo signal can be isolated and evaluated. Although such an evaluation is complicated by the contributory echoes reflected on the walls of the container or container installations, these contributory echoes can usually be differentiated from the echo of the material level due to the fact that the former only change over time if the surface reflecting the echo is either covered by the material or uncovered again. This means that the echo of the material level can, in the long term, be differentiated from interference echoes due to the fact that the transit time is variable in the long term with respect to the former [material] contributory echo; with respect to the latter [interference] contributory echo, the transit time remains unchanged, but its amplitude varies.
When such a container is filled, the echo signal relations are changed. Dust particles or material particles suspended in the air may cause a signal attenuation. The amplitude of the interference echo signals and the echo signal of the material level are changed; material may adhere to the container walls or fall off said container walls such that information on contributory interference echoes obtained at an earlier time is not necessarily valid during and after the filling process. If the signals used consist, in particular, of acoustic signals, the noise of the filling process may be superimposed with the echo signals and mask contributory echoes. Also, the flow of material being introduced into the container may also be the cause of interference echo signals if the emitted signal is reflected by this inflow.
Due to all these interfering influences, a level measurement by means of an echo signal that is evaluated with algorithms that provide satisfactory results may lead to usable results if the measurement is carried out while the container is filled. In order to ensure a constant and reliable level measurement, it is necessary to utilize different algorithms or parameters for estimating the level from the echo signal, namely in dependence on the fact of whether or not a filling process currently takes place.
If the evaluation of the echo signals should be automatically carried out in an evaluation unit, it is necessary that the evaluation unit not only receive the echo signal, but also information as to the fact of whether or not a filling process currently takes place. This type of information may, for example, be obtained by tapping a control signal that controls the open or closed state of a container filling closure element, from a control device of the filling closure element or by a position sensor arranged on the element. In both instances, it is necessary to prepare the container or its control device for tapping the required signal or to perform structural changes on the container or its control device.
The present invention is based on the objective of disclosing a method for detecting a filling process in a container and a device for carrying out said method which eliminate the necessity to prepare or perform structural changes on the container.
This objective is attained with a method that comprises the following steps
a) a signal is emitted into the container and the echo reflected from the container is recorded,
b) parameters of the reflected echo signals are determined, and
c) a filling process is detected if the parameters lie outside expected ranges,
wherein a device with a transceiver unit is provided for carrying out step a, and wherein an evaluation unit is provided for carrying out steps b and c.
In order to practically define the limits of the expected ranges, it is preferred to carry out measurements of the respective parameters while no filling process takes place, with the expected ranges being defined based on the thusly obtained typical parameter values while no filling of the container takes place.
These measurements can be carried out at various levels of the container. The parameters preferably are generated automatically during the operation once the device is installed.
The parameters for evaluating whether or not a filling process takes place preferably consist of amplitude values of the echo signals. According to one simple embodiment of the method, the parameter may consist of at least one amplitude value that is respectively measured within a given time after the signal is emitted. The amplitude value may, however, also be averaged over the entire time history or one or more intervals of the time history of the echo in order to improve the reliability of this evaluation.
Another suitable parameter consists of the degree of the amplitude fluctuations over the time history of the echo signals. These amplitude fluctuations are relatively small if the echo signals are superimposed with a loud noise caused by the filling process or if the echo signals reflected from the container are attenuated by the flow of material being introduced into the container.
Such a parameter can be easily obtained by adding the differences between amplitude measuring values of the echo signals which are recorded at successive times.
Since the echo amplitude usually drops over time after the signal is emitted, it is practical to only add the differences in which the amplitude of the later measuring value is higher than that of the earlier measuring value during the calculation of the parameter. Another option consists of forming a weighted sum of echo signal amplitude values at different times. In this case, an increasing weighting factor is preferably chosen over the time history of the echo signal.
Naturally, it is also possible to determine whether a filling process takes place or not by determining a series of parameters of the reflected echo, wherein a filling process is detected if at least a predetermined number of parameters lies outside the respective expected range.
Other characteristics and advantages of the invention are discussed in the following description of embodiments which refers to the enclosed figures. Shown are: